THE GENOMIC STRUCTURE OF A NEW SIMIAN T-LYMPHOTROPIC VIRUS, STLV-PH969, DIFFERS FROM THAT OF HUMAN T-LYMPHOTROPIC VIRUS TYPE-I AND TYPE-II

A new simian T-lymphotropic virus, STLV-PH969, was recently isolated f rom a wild-born Hamadryas baboon. Previous analysis had revealed that it differs sufficiently from the other HTLV/STLVs to be considered a n ew type, provisionally designated primate T-lymphotropic virus-L. Here we analyse a 3850 bp cDNA fragment spanning the 3' part of the STLV-P H969 genome. The fragment encodes three major proteins: Env, Tax and R ex. Sequence comparison and phylogenetic analysis indicate that in gen eral STLV-PH969 tends to be more closely related to HTLV-II than to HT LV-I, although separate gene regions might have evolved under differen t constraints. Detailed comparison of the Env, Tax and Rex proteins am ong the HTLV-I, -II and STLV-PH969 prototypes reveals that the amino a cid sequence of each protein shows a preferential conservation of func tionally important domains. RNA-PCR on cytoplasmic messengers demonstr ated splicing between a splice donor site immediately downstream of th e env start codon, and two splice acceptor sites identified in the pX region. The predominant spliced messenger encodes both Tax and Rex. Th e other messenger potentially encodes a new viral protein from the pro ximal part of the pX region that is similar in amino acid composition to p12(I) and p10(xI) of HTLV-I and HTLV-II respectively. This genomic organization of the proximal pX region of STLV-PH969 is different fro m that found in HTLV-I and HTLV-II. Therefore, the distinct classifica tion of this virus can be justified, not only in terms of sequence div ergence but also in terms of its different genomic structure.